Giardiasis and coccidiosis (Proceedings)


Giardia and Isospora spp coccidia are the protozoan parasites encountered most frequently in small animals.

Giardia and Isospora spp coccidia are the protozoan parasites encountered most frequently in small animals.  They are not closely related, but management of each can be problematic in some cases for the small animal practitioner.


Giardia is a common parasite of the canine and feline intestinal tract.  The organism exists in 2 forms:  the trophozoite, found in the small intestine, and the cyst, which is passed in the feces and is the form specialized for transmission. Giardia is far more common in the pet population than many veterinarians realize.  In a large survey of symptomatic dogs (16, 114 tested) and cats (4, 978 tested), 15.6% and 10.3%, respectively, were positive using the IDEXX Snap Giardia test (Carlin et al, 2006).  In another survey of over 1 million samples submitted to a commercial laboratory 4% of samples nationally were positive with over 6% positive in western states (Little et al, 2009).  The samples used in this study were all from the western US, which is generally thought to have a higher prevalence of Giardia than the rest of the country. 

All of the dogs that had positive samples in the western survey were considered asymptomatic by their veterinarian and it widely recognized that most animals infected with Giardia are not clinically affected or show signs only transiently.  High levels of infection are often encountered in kennels, breeding facilities or other areas with a high density of animals.  Because of the importance of waterborne sources of infection in humans, veterinarians sometimes assume that cats and dogs are primarily infected by that route, when more direct transmission from another infected animal may bemore likely.  Giardia cysts shed in the feces are immediately infective for another host and animal environments can be easily contaminated.

Dogs and cats that do develop signs of clinical giardiasis usuaully show signs of small bowel diarrhea that may be acute, chronic or intermittent.  In severe cases, diarrhea can be explosive and watery with accompanying malabsorption.  Giardia infection can be diagnosed either by microscopic detection of organisms in fecal samples or immunologically by detection of cyst antigen in the feces.  Many practices have relied on direct fecal smears for identification of Giardia trophozoites in feces of dogs and cats with diarrhea.  This is the least sensitive of the techniques available for diagnosis.  Trophozoites are never present in formed stool and are only occasionally present in diarrheic stool.  A far more sensitive test is the identification of Giardia cysts in fecal flotation tests.  In the diagnostic parasitology lab of the Virginia Tech hospital we only rarely find trophozoites in samples that have tested positive for cysts. 

We have found that a centrifugal fecal flotation test using 33% zinc sulfate flotation solution seems to be the most efficient flotation technique for recovery of cysts.  Using zinc sulfate flotation solution in a passive bench top flotation procedure is highly insensitive and inefficient for the recovery of all parasites.  Fecasol (sodium nitrate) solution rapidly distorts cysts and makes them more difficult to identify.  Unfortunately, although zinc sulfate flotation is quite effective in Giardia diagnosis, especially if 2 or 3 tests are performed, the organisms are small (cysts are about 12 µm in size) and unless the individual reading the slide is experienced, it is very likely that Giardia will be overlooked on a typical busy day, even when zinc sulfate flotation solution is used.  

The  Giardia SNAP® test (IDEXX) is a patient side test that detects a cyst wall Giardia antigen and does not rely on the presence of cysts in the feces. Comparisons have found good similarity between the results of the SNAP test and flotations performed by experienced microscopists, but no one method seems to be consistently better at detecting infection. For animals with clinical signs, it is recommended that both a centrifugal fecal flotation for cysts and an antigen test be performed. 

Treatment of clinically affected cats or dogs can be carried out with fenbendazole (50 mg/kg once daily for 3-5 days).  The commercial combination product febantel, pyrantel, and praziquantel can also be used because it contains febantel, which is metabolized to fenbendazole.  Many veterinarians use metronidazole (22 mg/kg orally twice daily for 5 days).  Metronidazole has a lower safety margin than fenbendazole and should not be given for extended periods or used at high doses. 

If desired, fenbendazole and metronidazole can be used together.  Some animals present repeatedly with giardiasis, frustrating owners and veterinarians.  Whether these cases represent incomplete drug treatment or reinfection is not clear, but every effort should be made to prevent reinfection, including bathing animals following treatment, cleaning the environment and treatment of other animals in the household.  Dogs and cats in crowded environments or suffering from other diseases or stress will also be more prone to infection.

The importance of asymptomatic Giardia infection is largely determined by its zoonotic potential and our understanding of that potential has been changing in the light of molecular analysis of isolates from a variety of animal species.  Currently, Giardia isolates are placed in one of several “assemblages.”  Assemblages C and D seem to be specific to dogs and Assemblage F appears to occur only in cats, but assemblages A and B infect both humans and a variety of other animals.  The proportions of the assemblages in isolates from companion animals seems to vary considerably with geographic region and a recent paper found a high prevalence of infection with zoonotic strains in asymptomatic dogs from the western US (Covacin et al, 2011).  However, our understanding of the natural history of Giardia is still quite limited and the actual risk presented by contact with these infected animals is unknown.  Because of our limited understanding, it is reasonable to treat asymptomatic animals if Giardia is detected.



Canine and feline coccidiosis are caused by species of Isospora (Cystisospora).  Coccidia are very common, species specific organisms and cross infection between dogs and cats and other species does not occur.  It can be assumed that all dogs and cats are probably exposed to coccidia oocysts at an early age.  Oocysts can withstand a variety of environmental conditions and are very difficult to eliminate.  As infection cycles through animals, immunity develops.  Adult animals may shed oocysts but rarely develop disease.  Clinical coccidiosis is a syndrome of acute diarrhea that typically develops in recently weaned kittens or puppies or those that have been moved to a new home.  Isospora infections are not a cause of chronic diarrhea unless there are other complicating factors.  Diagnosis of coccidiosis is supported by finding oocysts on a fecal exam, although clinical signs may precede a positive fecal exam. 

Table 1. Selected treatments for Isospora Infection in Dogs and Cats





50-60 mg/kg daily for 5-20 days



150 or 200 mg/kg daily for 6 days

100-200 mg/kg every 8 hours for 5 days



Dose/length depend on sulfa

>4 kg 30-60 mg/kg trimethoprim daily for 6 days

<4 kg 15-30 mg/kg trimethoprim for 6 days




20 mg/kg daily for 1-3 days

50 mg/kg for 1 day

30 mg/kg weekly for 2 treatments



25 mg/kg daily for 1 day



300-400 mg (total) for 5 days or 110-200 mg (total) daily for 7-12 days or 60-100 mg/kg (total) daily for 7 days

1.5 tablespoons (23 ml)/gallon (sole water source) not to exceed 10 days



150 mg/kg amprolium and 25 mg/kg  sulfadimethoxine for 14 days



8-20 mg/kg once or twice daily for 5 days


From Dubey et al, 2011.

Clinical coccidiosis is usually treated with sulfadimethoxine (Table 1).  Recently, some practitioners have begun using ponazuril for treatment, although this product is only approved for the treatment of equine protozoal myeloencephalitis in horses.  An occasional oocysts in the feces of a clinically normal dog or cat does not require treatment in most situations.  It is also important to differentiate Eimeria oocysts that may be in small animal feces through coprophagy or predation  from those of Isospora.


Carlin EP, Bowman, DD, Scarlett JM, Garrett J, Lorentzen L.  2006.  Prevalence of Giardia in symptomatic dogs and cats throughout the United States as determined by the IDEXX SNAP Giardia Test,  Vet Therapeutics. 7:199-206.

Companion  Animal Parasite Council.  Recommendations on Giardiasis, August , 2011.

Covacin C, Aucoin DP, Elliot A, Thompson RCA. 2011.  Genotypic characterization of Giardia from domestic dogs in the USA.  Vet. Parasitology. 177:28-32.

Dubey JP, Lindsay DS, Lappin MR.  2009.  Toxoplasmosis and other intestinal coccidial infections in dogs and cat.  Vet Clin Small Anim. 39:1009-1034.

Lindsay DS, Mitchell SM, Zajac AM.  2005.  Coccidiosis in a dog.  NAVC Clinician's Brief.  3:45-46.

Little SE, Johnson EM, Lewis D, Jaklitsch RP, Payton ME, Blagburn BL, Bowman DD, Moroff S, Tams T, Rich L, Aucoin D. 2009.  Prevalence of intestinal parasites in pet dogs in the United States. Vet Parasitol.  166:144-152.

Payne, PA and Artzer, M.  2009.  The biology and control of Giardia spp and Tritrichomas foetus.  Vet Clin Small Anim. 39:993-1007.

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